arXiv subjects

Anna N. Morozovska

Publications and source records attributed to Anna N. Morozovska.

At least 37 records · Page 2Linked to original sources

arXiv2025

Domain Morphology, Electrocaloric Response, and Negative Capacitance States of Ferroelectric Nanowires Array

We analyzed the domain morphology, electrocaloric response, and negative capacitance states in a one-dimensional array of uniformly oriented, radial symmetric ferroelectric nanowires, whose spontaneous polarization is normal to their symmetry axis. The wires are densely packed between flat electrodes. Using finite element modeling based on the Landau-Ginzburg-Devonshire approach, electrostatics, and elasticity theory, we calculated the distributions of spontaneous polarization, domain structures, electric potential, electric field, dielectric permittivity, and electrocaloric response in the nanowires. Due to size and depolarization effects, the paraelectric and ferroelectric (poly-domain or single-domain) states of the wires can be stable, depending on their radius and the dielectric permittivity of the surrounding medium. It is demonstrated that dipole-dipole interaction between the nanowires determines the stability of the polar (or anti-polar) state in the array when the wire radius is significantly smaller than the critical size of the paraelectric transition in an isolated wire. We reveal that a large region of a mixed state, characterized by poly-domain ferroelectric states with nonzero average polarization inside each wire and zero average polarization of the whole array, can be stable. By selecting the dielectric permittivity of the surrounding medium and the nanowire radius, one can maximize the negative capacitance effect in the capacitor with densely packed wires. It is also possible to achieve maximal enhancement of the electrocaloric response due to size effects in the wires. The underlying physics of the predicted enhancement is the combined action of size effects and the long-range electrostatic interactions between the ferroelectric dipoles in the nanowires and the image charges in the electrodes

cond-mat.mtrl-sci↗

arXiv2025

Colossal dielectric response of HfxZr1-xO2 nanoparticles

We reveal a colossal dielectric response of small (5 - 10 nm) oxygen-deficient HfxZr1-xO2 nanoparticles (x = 1 - 0.4), prepared by the solid-state organonitrate synthesis. The effective dielectric permittivity of the pressed HfxZr1-xO2 nanopowders has a pronounced maximum at 38 - 88 C, which shape can be fitted by the Curie-Weiss type dependence modified for the diffuse ferroelectric-paraelectric phase transition. The maximal value of the dielectric permittivity increases from 1.5*10^3 (for x = 1) to 1.5*10^5 (for x= 0.4) at low frequencies (~4 Hz); being much smaller, namely changing from 7 (for x = 1) to 20 (for x = 0.4) at high frequencies (~500 kHz). The frequency dispersion of the dielectric permittivity maximum position is almost absent, meanwhile the shape and width of the maximum changes in a complex way with increase in frequency. The temperature dependencies of the dielectric permittivity and resistivity are almost mirror-like turned over in respect to each other, which means that all their features, such as position and shape of maxima, plateau, minima and inflexions, almost coincide after the mirror reflection in respect to the temperature axis. These correlations of resistivity and dielectric permittivity are well-described in the Heywang barrier model applied together with the variable range hopping conduction model in semiconducting ferroelectrics. The ferroelectric-like behavior of the small oxygen-deficient HfxZr1-xO2 nanoparticles is expected from the Landau-Ginzburg-Devonshire approach and density functional theory calculations. Obtained results may be useful for developing silicon-compatible functional nanomaterials based on HfxZr1-xO2 nanoparticles.

cond-mat.mtrl-sci↗

arXiv2025

Tip-Based Proximity Ferroelectric Switching and Piezoelectric Response in Wurtzite Multilayers

Proximity ferroelectricity is a novel paradigm for inducing ferroelectricity, where a non-ferroelectric polar material, which is unswitchable with an external field below the dielectric breakdown field, becomes a practically switchable ferroelectric in direct contact with a thin switchable ferroelectric layer. Here, we develop a Landau-Ginzburg-Devonshire approach to study the proximity effect of local piezoelectric response and polarization reversal in wurtzite ferroelectric multilayers under a sharp electrically biased tip. Using finite element modeling we analyze the probe-induced nucleation of nanodomains, the features of local polarization hysteresis loops and coercive fields in the Al1-xScxN/AlN bilayers and three-layers. Similar to the wurtzite multilayers sandwiched between two parallel electrodes, the regimes of "proximity switching" (where the multilayers collectively switch) and the regime of "proximity suppression" (where they collectively do not switch) are the only two possible regimes in the probe-electrode geometry. However, the parameters and asymmetry of the local piezo-response and polarization hysteresis loops depend significantly on the sequence of the layers with respect to the probe. The physical mechanism of the proximity ferroelectricity in the local probe geometry is a depolarizing electric field determined by the polarization of the layers and their relative thickness. The field, whose direction is opposite to the polarization vector in the layer(s) with the larger spontaneous polarization (such as AlN), renormalizes the double-well ferroelectric potential to lower the steepness of the switching barrier in the "otherwise unswitchable" polar layers. Tip-based control of domains in otherwise non-ferroelectric layers using proximity ferroelectricity can provide nanoscale control of domain reversal in memory, actuation, sensing and optical applications.

cond-mat.mtrl-sci↗

arXiv2025

Proximity Ferroelectricity in Compositionally Graded Structures

Proximity ferroelectricity is a novel paradigm for inducing ferroelectricity in a non-ferroelectric polar material such as AlN or ZnO that are typically unswitchable with an external field below their dielectric breakdown field. When placed in direct contact with a thin switchable ferroelectric layer (such as Al1-xScxN or Zn1-xMgxO), they become a practically switchable ferroelectric. Using the thermodynamic Landau-Ginzburg-Devonshire theory, in this work we performed the finite element modeling of the polarization switching in the compositionally graded AlN-Al1-xScxN, ZnO-Zn1-xMgxO and MgO-Zn1-xMgxO structures sandwiched in both a parallel-plate capacitor geometry as well as in a sharp probe-planar electrode geometry. We reveal that the compositionally graded structure allows the simultaneous switching of spontaneous polarization in the whole system by a coercive field significantly lower than the electric breakdown field of unswitchable polar materials. The physical mechanism is the depolarization electric field determined by the gradient of chemical composition "x". The field lowers the steepness of the switching barrier in the otherwise unswitchable parts of the compositionally graded AlN-Al1-xScxN and ZnO-Zn1-xMgxO structures, while it induces a shallow double-well free energy potential in the MgO-like regions of compositionally graded MgO-Zn1-xMgxO structure. Proximity ferroelectric switching of the compositionally graded structures placed in the probe-electrode geometry occurs due to nanodomain formation under the tip. We predict that a gradient of chemical composition "x" significantly lowers effective coercive fields of the compositionally graded AlN-Al1-xScxN and ZnO-Zn1-xMgxO structures compared to the coercive fields of the corresponding multilayers with a uniform chemical composition in each layer.

cond-mat.mtrl-sci↗

arXiv2025

The impact of morphological structure and flexo-chemical strains on the electric transport mechanisms in the molybdenum-disulfide-oxide nanoflakes

Electric conduction mechanisms are studied in the pressed nanoflake powder of the molybdenum-disulfide-oxide (MoSxOy) depending on their content and structure. The MoSxOy nanoflakes were prepared by reaction of (NH4)6Mo7O24 with thiourea in aqueous solution followed by aerial oxidation. The sintered nanoflakes are 10-20 nm thick and self-assembled in the "nanoflower"-shape aggregates forming powder particles. The chemical composition and structure of the powders were studied by XPS, EDS and Raman spectroscopy, which show that the powders have different chemical composition and structure depending on the preparation conditions. These studies revealed the existence of different forms of MoS2 and its oxides in the powders. These features are impactful on electric transport properties. The current vs voltage (I-V) dependences of the pressed MoSxOy nanoflakes reveal hysteresis-like behavior; and their loop width depends on the chemical composition and structure. In the samples with the highest content of Mo in the oxide/sulfoxide form the negative differential conductivity has been observed. The I-V curves of all MoSxOy nanoflake samples manifest the three-state resistive switching and the long-lasting transient charge/discharge on switching "on/off" the voltage across the sample, which evidences the role of interface charges in their conductivity. To describe theoretically the observed I-V curves, polar and electric-transport properties of the pressed MoSxOy nanoflakes, the Landau-Cahn-Hilliard approach considering flexo-chemical field has been used. The revealed in experiment and explained theoretically features of resistive switching and charge accumulation look promising for applications in memristors and high-performance supercapacitors.

cond-mat.mtrl-sci↗

arXiv2025

The Influence of Electric Field on the Anisotropic Dispersion of the Flexocoupling Induced Phonons and Ferrons in Van der Waals Ferrielectrics

As has been shown recently, the influence of the flexoelectric coupling (shortly "flexocoupling") on the fluctuations of electric polarization and elastic strains can lead to the principal changes of the dispersion law of soft optical and acoustic phonons (shortly "flexophonons") and ferrons (shortly "flexoferrons") in van der Waals ferrielectrics. Analytical results, derived in the framework of Landau-Ginzburg-Devonshire approach, revealed that the dispersion of flexophonons and flexoferrons is strongly anisotropic and should depend on the magnitude and direction of applied electric field. In this work we study the influence of applied electric field on the anisotropic dispersion of the flexophonons and flexophonons in a uniaxial van der Waals ferrielectric CuInP2S6. We reveal that the frequency of acoustic flexophonons and flexoferrons tends to zero at nonzero wavevectors under increase of applied electric field. We relate the changes with a possible appearance of a spatially modulated incommensurate polar phase induced by the flexocoupling in external field. The critical strength of flexocoupling is determined by the magnitude of electric field and direction of the wavevector. This allows us to propose a method for estimating the strength of flexocoupling in van der Waals ferrielectrics, providing that the frequency of the acoustic flexophonon is zeroing at the threshold value of the electric field. Since the flexoelectric coefficients are poorly known in van der Waals ferrielectrics, obtained analytical results can be useful for their flexo-engineering.

cond-mat.mtrl-sci↗

arXiv2025

Dynamics of charge states at the surface of a ferroelectric nanoparticle in a liquid crystal

The liquid crystal with suspended ferroelectric nanoparticles is an interesting object for fundamental research of the long-range dipole-dipole interactions; as well as it is promising for optical, optoelectronic and electrochemical applications. Such suspensions can serve as basic elements for advanced nonvolatile memory cells and energy storage devices. The work studies the cells filled with a nematic liquid crystal 5CB and the cells containing 5CB with 0.5 wt.% and 1 wt.% of BaTiO3 nanoparticles with an average size of 24 nm. We analyzed the time dependences of the current flowing through the cells at constant applied voltage and the voltage dynamics in the no-load mode. The time dependences of the current and voltage show a slowing down decay rate. For the cells with BaTiO3 nanoparticles, the decrease in the decay time is characteristic. A possible physical reason for the retarding decay time rate is the indirect effect of screening charges, which cover ferroelectric nanoparticles, and slow ionic transport in the liquid crystal. To explain the dynamics of current and voltage, the finite element modeling of the polarization distribution, domain structure dynamics, and charge state of nanoparticles in a liquid crystal is performed using Landau-Ginzburg-Devonshire approach. Theoretical results confirmed the leading role of screening charges, because the surface of a ferroelectric nanoparticle adsorbs an ionic-electronic charge that partially screens its spontaneous polarization in single-domain and/or poly-domain states. When an electric field is applied to the liquid crystal with nanoparticles, it can release part of the screening charge (mainly due to the change in the polarization of the nanoparticle), which will lead to a decrease in decay time rate of the current and voltage dependences.

cond-mat.mtrl-sci↗

arXiv2025

Flexocoupling-induced phonons and ferrons in van der Waals ferroelectrics

The contribution of flexoelectric coupling to the long-range order parameter fluctuations in ferroics can be critically important to the ferron dispersion and related polar, pyroelectric and electrocaloric properties. Here we calculate analytically the dispersion relations of soft optic and acoustic flexocoupling-induced phonons and ferrons by incorporating the flexoelectric coupling, damping, and higher elastic gradients in the Landau-Ginzburg-Devonshire free energy functional using the van der Waals uniaxial ferrielectric CuInP2S6 as an example. We analyze the changes in the flexocoupling-induced phonon and ferron spectra arising from the appearance of spatially modulated phases induced by the flexoelectric coupling. We show that the free energy landscape of CuInP2S6 determines the specific features of its phonon spectra and ferron dispersion. We also discuss the contributions of optic and acoustic flexocoupling-induced ferrons to the pyroelectric and electrocaloric responses of CuInP2S6 at low temperatures.

cond-mat.mtrl-sci↗

arXiv2025

Polarization switching on the open surfaces of the wurtzite ferroelectric nitrides: ferroelectric subsystems and electrochemical reactivity

Binary ferroelectric nitrides are promising materials for information technologies and power electronics. However, polarization switching in these materials is highly unusual. From the structural perspective, polarization reversal is associated with the change of the effective polarity at the surfaces and interfaces from N-to-M terminated, suggesting strong coupling between ferroelectric and chemical phenomena. Phenomenologically, macroscopic studies demonstrate the presence of complex time dependent phenomena including wake-up. Here, we explore the polarization switching using the multidimensional high-resolution piezoresponse force microscopy (PFM) and spectroscopy, detecting both the evolution of induced ferroelectric domain, electromechanical response, and surface deformation during first-order reversal curve measurements. We demonstrate the presence of two weakly coupled ferroelectric subsystems and the bias-induced electrochemical reactivity. The observed behaviors are very similar to the recent studies of other wurtzite system but additionally include electrochemical reactivity, suggesting the universality of these behaviors for the wurtzite binary ferroelectrics. These studies suggest potential of high-resolution multimodal PFM spectroscopies to resolve complex coupled polarization dynamics in materials. Furthermore, these PFM based studies are fully consistent with the recent electron microscopy observations of the shark-teeth like ferroelectric domains in nitrides. Hence, we believe that these studies establish the universal phenomenological picture of polarization switching in binary wurtzite.

cond-mat.mtrl-sci↗

arXiv2025

Resistive switching and charge accumulation in Hf0.5Zr0.5O2 nanoparticles

We revealed the resistive switching, negative differential resistance and charge accumulation effects in Hf0.5Zr0.5O2 nanopowders sintered by the auto-combustion sol-gel method and annealed at temperatures from 500°C to 800°C. The fraction of the orthorhombic phase, determined by the X-ray diffraction (XRD), decreases from 91 vol.% to 7 vol.% with an increase in the annealing temperature from 600°C to 800°C. The electron paramagnetic resonance (EPR) spectra reveal the great amount of oxygen vacancies in the annealed samples, at that the decrease of the orthorhombic phase fraction (observed with an increase in the annealing temperature) correlates with a decrease in the intensity of EPR spectral lines associated with the oxygen vacancies and impurities. This indicates the participation of oxygen vacancies and other defects in the formation of the orthorhombic phase in the Hf0.5Zr0.5O2 powders. To explain the results of electrophysical measurements, we compare the features of the current-voltage characteristics with the phase composition of the Hf0.5Zr0.5O2 powders and with the peculiarities of their EPR spectra. The analysis allows us to relate the resistive switching and charge accumulation observed in Hf0.5Zr0.5O2 nanopowders with the appearance of the ferroelectric-like polar regions in the orthorhombic phase of the nanoparticles, which agrees with the calculations performed in the framework of Landau-Ginzburg-Devonshire approach and density functional theory.

cond-mat.mtrl-sci↗

arXiv2025

The Role of Flexoelectric Coupling and Chemical Strains in the Emergence of Polar Chiral Nano-Structures

This review examines the conditions that lead to the formation of flexo-sensitive chiral polar structures in thin films and core-shell ferroelectric nanoparticles. It also analyzes possible mechanisms by which the flexoelectric effect impacts the polarization structure in core-shell ferroelectric nanoparticles. Special attention is given to the role of the anisotropic flexoelectric effect in forming a unique type of polarization states with distinct chiral properties, referred to as "flexons". In the first part of the review, we study the influence of the flexoelectric coupling on the polarity, chirality and branching of metastable labyrinthine domain structures in uniaxial ferroelectric core-shell nanoparticles. We reveal that the transition from sinuous branched domain stripes to spiral-like domains occurs gradually as the flexoelectric coupling strength is increased. Our findings indicate that the joint action of flexoelectric effect and chemical strains, termed as "flexo-chemical" coupling, can significantly influence the effective Curie temperature, polarization distribution, domain morphology, and chirality in multiaxial ferroelectric core-shell nanoparticles. Furthermore, we demonstrate that the combination of flexo-chemical coupling and screening effects leads to the appearance and stabilization of a chiral polarization morphology in nanoflakes of van der Waals ferrielectrics. In the second part of the review, we discuss several advanced applications of flexo-sensitive chiral polar structures in core-shell ferroelectric nanoparticles for nanoelectronics elements and cryptography. We underline the possibilities of the flexoelectric control of multiple-degenerated labyrinthine states, which may correspond to a differential negative capacitance (NC) state stabilized in the uniaxial ferroelectric core by the presence of a screening shell.

cond-mat.mtrl-sci↗

arXiv2025

Strain-Gradient and Curvature-Induced Changes in Domain Morphology of BaTiO3 Nanorods: Experimental and Theoretical Studies

We investigate the impact of OH- ions incorporation on the lattice strain and spontaneous polarization of BaTiO3 nanorods synthesized under different conditions. It was confirmed that the lattice strain depends directly on Ba supersaturation, with higher supersaturation leading to an increase in the lattice strain. However, it was shown that crystal growth and observed lattice distortion are not primarily influenced by external strain; rather, OH- ions incorporation plays a key role in generating internal chemical strains and driving these processes. By using the less reactive TiO2 precursor instead of TiOCl2 and controlling Ba supersaturation, the slower nucleation rate enables more effective regulation of OH- ions incorporation and crystal growth. This in turn effects both particle size and lattice distortion, leading to c/a ratio of 1.013 - 1.014. The incorporation of OH- ions induces lattice elongation along the c-axis, contributing to anisotropic growth, increasing of the rod diameter and their growth-induced bending. However, the possibility of the curvature-induced changes in domain morphology of BaTiO3 nanorods remains almost unexplored. To study the possibility, we perform analytical calculations and finite element modeling, which provide insights into the curvature-induced changes in the strain-gradient, polarization distribution, and domain morphology in BaTiO3 nanorods. Theoretical results reveal the appearance of the domain stripes in BaTiO3 nanorod when the curvature exceeds a critical angle. The physical origin of the domain stripes emergence is the tendency to minimize its elastic energy of the nanorod by the domain splitting. These findings suggest that BaTiO3 nanorods, with curvature-controllable amount of domain stripes, could serve as flexible race-track memory elements for flexo-tronics and domain-wall electronics.

cond-mat.mtrl-sci↗

arXiv2025

A Thermodynamic Theory of Proximity Ferroelectricity

Proximity ferroelectricity has recently been reported as a new design paradigm for inducing ferroelectricity, where a non-ferroelectric polar material becomes a ferroelectric by interfacing with a thin ferroelectric layer. Strongly polar materials, such as AlN and ZnO, which were previously unswitchable with an external field below their dielectric breakdown fields, can now be switched with practical coercive fields when they are in intimate proximity to a switchable ferroelectric. Here, we develop a general Landau-Ginzburg theory of proximity ferroelectricity in multilayers of non-ferroelectrics and ferroelectrics to analyze their switchability and coercive fields. The theory predicts regimes of both "proximity switching" where the multilayers collectively switch, as well as "proximity suppression" where they collectively do not switch. The mechanism of the proximity ferroelectricity is an internal electric field determined by the polarization of the layers and their relative thickness in a self-consistent manner that renormalizes the double-well ferroelectric potential to lower the steepness of the switching barrier. Further reduction in the coercive field emerges from charged defects in the bulk that act as nucleation centers. The application of the theory to proximity ferroelectricity in Alx-1ScxN/AlN and Zn1-xMgxO/ZnO bilayers is demonstrated. The theory further predicts that multilayers of dielectric/ferroelectric and paraelectric/ferroelectric layers can potentially result in induced ferroelectricity in the dielectric or paraelectric layers, resulting in the entire stack being switched, an exciting avenue for new discoveries. This thawing of "frozen ferroelectrics", paraelectrics and potentially dielectrics, promises a large class of new ferroelectrics with exciting prospects for previously unrealizable domain-patterned optoelectronic and memory technologies.

cond-mat.mtrl-sci↗

arXiv2025

Interfacial Effects and Negative Capacitance State in P(VDF-TrFE) Films with BaTiO3 Nanoparticles

We analyze the temperature dependences of the effective dielectric permittivity of P(VDF-TrFE) films with BaTiO3 nanoparticles (with the average size 24 nm). Transition from a weak to a strong nonlinear temperature dependence of the dielectric permittivity is observed near the freezing temperature (near -50 °C) of P(VDF-TrFE). The transition is followed by a diffuse step-like change in the temperature range (0 - 40)°C, and a subsequent maximum of the dielectric permittivity in the P(VDF-TrFE) films with a lower content (~20-40 vol.%) of BaTiO3 nanoparticles; or by a quasi-plateau of the dielectric permittivity in the P(VDF-TrFE) films with a higher content (~ 50-70 vol.%) of BaTiO3 nanoparticles. The frequency dispersion of the dielectric permittivity is significant in the vicinity of its maxima. The temperature-frequency shift of the permittivity region with a strong temperature dependence is positive. The temperature-frequency shift of the maxima is insignificant (or negative) for the P(VDF-TrFE) films with lower content of BaTiO3 nanoparticles. Increasing the content of BaTiO3 nanoparticles leads to a significant increase in the relative dielectric permittivity of the P(VDF-TrFE)-BaTiO3 films compared to pure P(VDF-TrFE) films (from 8 to 50 at 25 °C). At the same time, the voltage response of the studied P(VDF-TrFE)/BaTiO3 films to the frequency-modulated IR radiation flux has rather photoelectric than pyroelectric nature. A phenomenological model, which considers the screening charges at the interfaces, as well as dipole-dipole cross-interaction effects between the ferroelectric nanoparticles, is proposed to describe the temperature and frequency behavior of the effective dielectric permittivity. The negative capacitance state, which originates due to the interfacial effects, is predicted in the P(VDF-TrFE) films with a high content of BaTiO3 nanoparticles.

cond-mat.mtrl-sci↗

arXiv2025

Adsorption of ions from aqueous solutions by ferroelectric nanoparticles

The fundamental aspect of physics of ferroelectric materials is the screening of uncompensated bound charges by the dissociative adsorption of ionic charges from the environment. The adsorption of ions can be especially strong when the ferroelectric undergoes the temperature-induced transition from the paraelectric phase to the ferroelectric state. Here we demonstrate that the adsorption of ions and free radicals by the polar surface of ferroelectric nanoparticles can be very efficient in aqueous solutions due to the strong ferro-ionic coupling in the nanoparticles. Obtained results can be useful for the elaboration of alternative methods and tools for adsorption of the cations (Li+, K+, Na+, etc.), anions (Cl-, Br-, J-), and/or free radicals (CO-, NH4+, etc.) from aqueous solutions by the lead-free uniaxial ferroelectric nanoparticles. The results may become an alternative way for the environment-friendly laboratory-scale purification of different aqueous solutions from ionic contamination using controllable cyclic temperature variations.

cond-mat.mtrl-sci↗

arXiv2024

The origin of the ferroelectric-like orthorhombic phase in oxygen-deficient HfO2-y nanoparticles

In this work we established the relationship between the crystalline structure symmetry, point defects and possible appearance of the ferroelectric-like polarization in HfO2-y nanoparticles. Notably, that XRD and EPR analysis revealed the formation of the ferroelectric-like orthorhombic phase in the oxygen-deficient HfO2-y nanoparticles (pure and doped with rare-earth element yttrium). DFT calculations showed that small HfO2 nanoparticles may become polar, especially in the presence of impurity atoms and/or oxygen vacancies. To explain the experimental results, we have modified the effective LGD model through the parameterization approach, focusing on the Landau expansion coefficients associated with the polar (FE) and antipolar (AFE) orderings, which agrees with the performed DFT calculations. The effective LGD model can be useful for the development of the novel generation of silicon-compatible ferroelectric nanomaterials based on the HfxZr1-xO2-y.

cond-mat.mtrl-sci↗

arXiv2024

Reentrant polar phase induced by the ferro-ionic coupling in Bi$_{1-x}$Sm$_x$FeO$_3$ nanoparticles

Using the model of four sublattices, the Landau-Ginzburg-Devonshire-Kittel phenomenological approach and the Stephenson-Highland ionic adsorption model for the description of coupled polar and antipolar long-range orders in ferroics, we calculated analytically the phase diagrams and polar properties of Bi$_{1-x}$Sm$_x$FeO$_3$ nanoparticles covered by surface ions in dependence on their size, surface ions density, samarium content "x" and temperature. The size effects and ferro-ionic coupling govern the appearance and stability conditions of the long-range ordered ferroelectric, reentrant ferrielectric and antiferroelectric phases in the Bi1-xSmxFeO3 nanoparticles. Calculated phase diagrams are in a qualitative agreement with the X-ray diffraction phase analysis, electron paramagnetic resonance, infra-red spectroscopy and electrophysical measurements of the Bi$_{1-x}$Sm$_x$FeO$_3$ nanopowders sintered by the solution combustion method. The combined theoretical-experimental approach allows to establish the influence of the ferro-ionic coupling and size effects in Bi$_{1-x}$Sm$_x$FeO$_3$ nanoparticles on their polar properties.

cond-mat.mtrl-sci↗

arXiv2024

Anomalous Behavior of the Dielectric and Pyroelectric Responses of Ferroelectric Fine-Grained Ceramics

We revealed the anomalous temperature behavior of the giant dielectric permittivity and unusual frequency dependences of the pyroelectric response of the fine-grained ceramics prepared by the spark plasma sintering of the ferroelectric BaTiO3 nanoparticles. The temperature dependences of the electro-resistivity indicate the frequency-dependent transition in the electro-transport mechanisms between the lower and higher conductivity states accompanied by the maximum in the temperature dependence of the loss angle tangent. The pyroelectric thermal-wave probing revealed the existence of the spatially inhomogeneous counter-polarized ferroelectric state at the opposite surfaces of the ceramic sample. We described the temperature behavior of the giant dielectric response and losses using the core-shell model for ceramic grains, effective medium approach and Maxwell-Wagner approach. The superparaelectric-like state with a giant dielectric response may appear due to the internal barrier-layer capacitance effect, while the step-like thermal activation of localized polarons in the semiconducting grains is not excluded. The elucidation of the state microscopic origin requires measurements in the frequency range above 1 MHz.

cond-mat.mtrl-sci↗